1. Field of the Invention
The present invention relates to a system and a method for managing a state of a communication using an intelligent network, and more particularly to a system and a method for managing a state of a communication using an intelligent network which provides a service to convert a predetermined number which is preregistered into a number identifying a destination.
2. Description of the Related Art
An intelligent network is a communications network which has been popularized by meeting the demand for enhancing its capabilities, and an information transfer network and a service control network are arranged hierarchically.
The information transfer network is composed of electronic switches called SSPs (Service Switching Points), SAPs (Service Access Points), etc. Each of the SSPs is intended to transfer a service request from a subscriber to a service control network, and to control a communications network according to an instruction given by the service control network.
The service control network normally includes servers called SCPs (Service Control Points) or NSPs (Network Service Control Points). Each of the SCPs includes an integrated database which normally stores subscriber information, network configuration information, service control software, etc., and integrates communications service capabilities such as a communication processing capability, service providing capability, path selection control capability, etc. The SCP provides a service (required communication control information) in response to a request made by the SSP.
FIG. 1 is a schematic diagram showing the configuration of a typical intelligent network. An SCP 101 and SSPs 102-1 through 102-n are connected via a switching node for a common channel signaling network, called an STP (Signaling Transfer Point) 103. Each of the SSPs 102-1 through 102-n transmits a service request to the SCP 101 via the STP 103, while the SCP 101 provides a service (required communication control information) to each of the SSPs 102-1 through 102-n via the STP 103, in response to the service request.
The intelligent network provides enhanced services such as putting a number system into a virtual form (logical form), enhanced routing control, flexible interconnection control, variable operation of a communications network, etc.
One of the services provided by the intelligent network is a service for converting a telephone number, represented by a toll-free number telephone service. Provided below is the explanation about an example of the number conversion service. Here, a service for changing a destination depending on the availability of a subscriber at a destination such as an FRS (Flexible Routing Service), is raised.
The SCP 101 includes a management table (database) 111 shown in FIG. 2A in order to provide the number conversion service. In this figure, "IN telephone number" is a virtual number contracted in advance. "converted telephone number" is a telephone number of an actual and normal subscriber. If a subscriber inputs a certain IN telephone number, that call is connected to any of terminals having converted telephone numbers corresponding to the input IN telephone number. "state" indicates whether a terminal (line) identified by a converted telephone number is either busy or idle.
If a subscriber "A" accommodated in the SSP 102-1 inputs an IN telephone number 0120-044-123, the SSP 102-1 transmits the IN number to the SCP 101 to request convertion of the number. When receiving this request, the SCP 101 searches for a management table 111, retrieves a converted telephone number in the idle state (for example, 044-123-4567) from converted telephone numbers corresponding to that IN number, and returns the retrieved number to the SSP 102-1. At this time, the SCP 101 changes the state of the retrieved number to the "busy" state in the management table 111.
Each of the SSPs 102-1 through 102-n includes a management table 112 shown in FIG. 2B. "line identification number" is a number for identifying a line accommodated in each of the SSPs 102-1 through 102-n. "receiver number" is a telephone number of a receiver of a terminal connected to a line identified by the line identification number. "state" indicates whether or not the line identified by the line identification number, or a terminal connected to that line, is busy.
When receiving the converted telephone number from the SCP 101, the SSP 102-1 establishes a call according to that number. The SSP 102-1 updates data regarding the subscriber A in the management table 112. Assuming that the line identification number of the line to which the subscriber A is connected is 002, the SSP 102-1 writes the converted telephone number which is received as the receiver number in correspondence with the line identification number, and updates its state to "busy".
If the subscriber A releases the call, the SSP 102-1 clears the receiver number in the management table 112, and updates its state to "idle". In the meantime, the SCP 101 updates the state of the converted telephone number 044-123-4567 to "idle" in the management table 111, when receiving the notification that the call was released from the SSP 102-1.
As described above, the number conversion service such as an FRS is provided by arranging the management table 111 which manages an idle/busy state of a subscriber at a destination in the SCP 101.
The link between the SCP 101 and each of the SSPs 102-1 through 102-n, however, is not established all the time. It is established depending on need (for example, at an access made by a service request). Therefore, if a fault occurs in the SCP 101 or any of the SSPs 102-1 through 102-n, the contents of the management table 111 arranged in the SCP 101 may sometimes be inconsistent with an actual communication state of any of the SSPs 102-1 through 102-n, at the time of restoration from the fault.
Such an inconsistent state causes the following problem. By way of example, assume that the state of the telephone number 044-123-4567 is "busy" in the management table 111 arranged in the SCP 101, although a call between the subscriber A and the terminal having the telephone number 044-123-4567 (hereinafter referred to as a subscriber B), is released. Physically, the subscriber B can receive a call in this case. However, if a certain subscriber inputs the IN telephone number 0120-044-123, the SCP 101 regards the telephone number 044-123-4567 as being busy. Accordingly, the IN number 0120-044-123 is not converted into the telephone number 044-123-4567 in the number conversion service. That is, that line cannot be used even though the line of the subscriber B is actually available. As a result, the communication resource is not used properly.
The above described problem is due to an inconsistency between the contents of the management table 111 arranged in the SCP 101 and the actual communication state.
As a technique for monitoring the normality of the service between the SCP 101 and the SSPs 102-1 through 102-n, the invention "TOKKAIHEI 6-46129, for example, is known. This invention discloses a monitoring system for monitoring an entire network including an SCP and SSPs, and restarting the SCP or SSPs if a fault is detected. According to such a system for restarting the SCP or the SSPs, however, the service is forced to be halted. Specifically, if the SCP is restarted, it causes an undesirable phenomenon. That is, all of services are halted. Furthermore, a simple restart of the SCP or the SSPs cannot make the communication states that the SCP manages consistent with the actual communication states of the SSPs.